1. Field of the Invention
The present invention relates generally to automotive vehicle frames and, more specifically, to energy absorbing forward and rear portions of an automotive vehicle frame.
2. Description of the Related Art
It is known to construct frames for vehicles such as automotive vehicles defining the general shape of the automotive vehicle and for supporting its various load-bearing functional components from metal components fabricated in a variety of manners. In the interest of enhancing fuel economy of automotive vehicles, great attention has been given to fabricating vehicular components from light weight materials. On the other hand, a competing interest in the design of the vehicle frame is the dissipation of energy in the unfortunate event of a collision of the vehicle.
It is also known that vehicle frames include forward, rear and central portions. Generally, the forward and rear portions are designed to, among other things, absorb and dissipate energy in the event of a collision or impact of sufficient predetermined force on the automotive vehicle. The forward and rear portions typically include hollow, longitudinal rails which are often fabricated from structural members made of a steel material by spot welding the structural members together. In steel material, structural transformations occur during a cooling period after the spot weld has been formed which act to strengthen the spot weld itself so that it can be stronger than the surrounding base steel material.
One disadvantage of using steel material in structural members of the forward and rear portions of the vehicle frame is the increased weight in the overall vehicle frame and, therefore, the vehicle. Accordingly, attempts have been made to fabricate the structural members of the forward and rear portions of the vehicle frame from lighter materials such as aluminum, magnesium or alloys thereof. Aluminum or magnesium spot welds are soft and porous with more voids than steel materials. Unfortunately, the structural transformations which take place during the cooling period after spot welding steel materials do not take place after spot welding aluminum or magnesium materials.
For a given aluminum or magnesium material, it is known to increase the weld strength in the welded aluminum or magnesium structural members by increasing the size and number of the spot welds used. However, the thickness of the welded aluminum or magnesium structural members limits the maximum size of the spot weld which can be produced in any given situation. Further, reducing the number of spot welds in the welded aluminum or magnesium structural members is of particular relevance because of electrode contamination and the consequent shortening of tip life of the spot welder due to the electrical power used during spot welding.
Buckling and folding may occur during the collision of the welded aluminum or magnesium structural members. Unfortunately, it is quite possible for separation of the welded aluminum or magnesium structural members to occur before significant crush of these structural members has taken place. When welded structural members separate to create open form sections, the vehicle frame tends to have considerable reduced load bearing ability in comparison to closed form sections. In this case, weld separation can lead to a diminished energy absorption and dissipation performance.